Antimicrobial compositions

ABSTRACT

The present invention relates to a method of controlling microbial growth on a material or surface. The method includes applying to the material an antimicrobial agent including colloid particles having an ion exchange capacity and having attached a quantity of one or more ligands with antimicrobial properties where the quantity of ligand attached to the colloid particles is in excess of 100% and up to 200% of the ion exchange capacity of the colloid particles. The present invention also relates to a method of controlling mircobial growth in a material. In addition, the present invention relates to an antimicrobial surface, an antimicrobial material, and an antimicrobial agent.

This application is a continuation of U.S. patent application Ser. No.08/807,140, filed Feb. 27, 1997, now U.S. Pat. No. 6,015,816, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/012,513, filed Feb. 29, 1996.

FIELD OF THE INVENTION

This invention relates generally to an antimicrobial agent and tomethods of preventing microbial growth. In particular, the presentinvention involves an antimicrobial agent containing mineral colloidparticles which are modified with antimicrobial ligands.

BACKGROUND OF THE INVENTION

To control microbial growth on a surface, antimicrobials are applied tothe surface. Microbial growth in a material can also be controlled bymixing antimicrobials with the material.

One group of compounds commonly used for surface disinfection arequaternary ammonium compounds (“QACs”). The general formula for the QACsis as follows:

where R₁, R₂, R₃, and R₄ are alkyl groups which may be alike ordifferent. Structurally, these compounds contain four carbon atomslinked directly to one nitrogen atom through covalent bonds. The portionattached to the nitrogen by an electrovalent bond may be any anion, butit is usually chloride or bromide to form the salt. The nitrogen atomwith the attached alkyl groups forms the positively charged cationportion. Depending on the nature of the R groups, the anion and thenumber of quaternary nitrogen atoms present, the antimicrobialquaternary ammonium compounds may be classified as monoalkyltrimethyl,monoalkyldimethylbenzyl, heteroaromatic, polysubstituted quaternary,bis-quaternary, or polymeric quaternary ammonium compounds.

Quaternary ammonium compounds have been widely used for disinfection offloors, walls, and equipment surfaces in hospitals, nursing homes, andother public places. Disinfection of these surfaces is carried out byvarious means, such as an aerosol spray containing quaternary ammoniumcompounds or a mist of quaternary ammonium compound germicide generatedfrom commercial fogging devices. In addition, QACs have been used in thetreatment of food contact surfaces and in outdoor swimming pools andcooling water systems to prevent the proliferation of bacteria. John J.Merianos, “Quaternary Ammonium Antimicrobial Compounds”, inDisinfection, Sterilization and Prevention, 4th ed. Lea & Fabiger,Philadelphia (1991), which is hereby incorporated by reference.

When QACs are applied directly to surfaces, their effect is notlong-lasting due to leaching of the compound from the surface.Therefore, frequent applications may be needed to achieve prolongedantimicrobial effects. As a result, the use of QACs as antimicrobialshas not proven to be suitable for surfaces that are not accessible forrepeated applications.

The ability to modify the surface of smectite clay minerals by means ofa cation exchange with organic cations has been recognized since the1930s (Gieseking, J. E., “Mechanism of Cation Exchange in theMont-Morillonite-Beidellite-Nontronite Type of Clay Minerals,” SoilScience, 47:1-14 (1939), which is hereby incorporated by reference). Thequantity of exchangeable cations available on the clay mineral surfacesis given by the cation exchange capacity (“C.E.C.”), which has units ofmilliequivalents (meq)/100 grams of clay. The C.E.C. of smectite claystypically varies between approximately 50 and 150 meq/100 grams. Thecation exchange is accomplished by dispersing the clay mineral in wateror a mixture of water and a miscible organic solvent such as alcohol inwhich is dissolved a quantity of the organic cation sufficient tosatisfy the C.E.C. of the clay mineral. The organic cation replaces theinorganic cation in a nearly quantitative manner by this singletreatment method.

Occasionally, clay minerals are treated with solutions containing anorganic cation at greater than the C.E.C. value (as disclosed in U.S.Pat. Nos. 4,116,866, 4,081,496, 4,105,578, and 4,287,086 to Finlayson;U.S. Pat. Nos. 4,365,030 and 4,317,737 to Oswald, et al.; and U.S. Pat.No. 4,929,644 to Guilbeaux; which are hereby incorporated by reference).However, treatment with an organic cation in excess of the C.E.C. doesnot ensure that the product will have the exchanged organic materialaffixed to the clay surfaces in excess of the C.E.C. To definitivelyestablish that the attached organic material exceeds the C.E.C., it isnecessary to analyze the quantity of organic material in the organo-clayproduct. This can be done by determining the carbon content of theproduct (Ohashi, et al., “Antimicrobial and Antifungal Agents DerivedFrom Clay Minerals: Part IV Properties of Montmorillonite Supported bySilver Chelate of Hypoxanthine,” J. Mat. Sci., 27:5027-30 (1992) andOhashi, et al., “Antimicrobial and Antifungal Agents Derived From ClayMinerals: Part VIII Thermostability of Montmorillonite Intercalated bySilver Chelate of 2-(4-thiazolyl)-benzimidazole or Quaternary AmmoniumSalts,” J. Mat. Sci., 31:3403-07 (1996), which are hereby incorporatedby reference) or by determining the weight loss upon high temperatureoxidation of the product.

The typical procedure used to form the organo-clay is to treat the claymineral by a single exposure to an aqueous solution of the organiccation whose total quantity in the solution is used to determine theC.E.C. equivalents bound to clay mineral (U.S. Pat. No. 4,365,030 toOswald, et al., which is hereby incorporated by reference).

The utility of organo-clay as antimicrobial compounds has been pointedout by several workers (Oya, et al., “An Antimicrobial and AntifungalAgent Derived From Montmorillonite,” Appl. Clay Sci., 6:135-42 (1991);Oya, et al., “Antimicrobial and Antifungal Agents Derived From ClayMinerals (III): Control of Antimicrobial and Antifungal Activities ofAg+-exchanged Montmorillonite by Intercalation of Polyacrylonitrile,”Appl. Clay Sci., 6:311-18 (1992); Ohashi, et al., “Antimicrobial andAntifungal Agents Derived From Clay Minerals (II): Properties ofMontmorillonite Supported by Silver Chelates of 1,10-phenanthroline and2,2′-dipyridyl,” Appl. Clay Sci., 6:301-10 (1992); and Ohashi, et al.,“Antimicrobial and Antifungal Agents Derived From Clay Minerals: PartVIII Thermostability of Montmorillonite Intercalated by Silver Chelateof 2-(4-thiazolyl)-bebzunudazole or Quaternary Ammonium Salts,” J. Mat.Sci., 31:3403-07 (1996), which are hereby incorporated by reference).These materials were fabricated by treating the smectite clay mineralwith an organic cation or a metal (silver) chelated with an organiccation, all at a quantity sufficient to satisfy the C.E.C. of the claymineral.

However, none of these references disclose a clay mineral having anorganic cation present in excess of the C.E.C. of the clay. Accordingly,the clay materials of the prior art are not entirely satisfactory ascompounds having antimicrobial activity.

The present invention is directed to overcoming these above-noteddeficiencies by disclosing a process which attaches an antimicrobialligand to the clay in excess of the C.E.C., thereby imparting increasedantimicrobial activity.

SUMMARY OF THE INVENTION

The present invention relates to a method of controlling microbialgrowth on a material which includes applying to the material anantimicrobial agent. The antimicrobial agent includes mineral colloidparticles having an ion exchange capacity and one or more ligands havingantimicrobial properties.

Another aspect of the present invention relates to a method ofcontrolling microbial growth in a material. The method includes mixingwith the material colloid particles having an ion exchange capacity andhaving one or more ligands having antimicrobial properties, where thequantity of the ligands attached to the colloid particles is in excessof and up to 200% of the ion exchange capacity of the colloid particles.

Yet another aspect of the present invention relates to an antimicrobialsurface coated with colloid particles having one or more ligands withantimicrobial properties.

Yet another aspect of the present invention relates to a material towhich antimicrobial properties have been imparted, where the materialcontains colloid particles having an ion exchange capacity and havingligands with antimicrobial properties, and where the quantity of theligands attached to the colloidal particles is in excess of and up to200% of the ion exchange capacity of the colloid particles.

Yet another aspect of the present invention relates to an antimicrobialagent which includes colloid particles having an ion exchange capacityand having one or more ligands with antimicrobial properties, where thequantity of the ligands attached to the colloidal particles is in excessof and up to 200% of the ion exchange capacity of the colloid particles.

Yet another aspect of the present invention relates to a complex havingcolloid particles having an ion exchange capacity and having one or moreligands, where the quantity of the ligands attached to the colloidalparticles is in excess of and up to 200% of the ion exchange capacity ofthe colloid particles.

The methods, surface, material, antimicrobial agents and colloidparticles of the present invention offer advantages not obtainable withthe prior art antimicrobials. Because the ligands having antimicrobialproperties are strongly bound to the colloid particles of the presentinvention, the ability of the ligand to leach out is limited. Thus, theantimicrobial agent retains its antimicrobial properties, and the needfor repeated coatings to a surface is eliminated or reduced. Inaddition, because the colloid particles containing a ligand havingantimicrobial property are inert, they are less toxic, resulting in easeof handling, use, and disposal. As a coating for a surface, theantimicrobial agent of the present invention is particularly desirable,because it is less costly to coat a surface of a material than to mixthe antimicrobial agent throughout the material. The use of theantimicrobial agent as an additive in a material, however, offers otheradvantages. For example, the antimicrobial agent of the presentinvention is useful as an inexpensive filler material. Further, when theantimicrobial agent is mixed throughout the material, as the surface ofthe material wears, fresh antimicrobial is exposed at the surface. Inaddition, the antimicrobial agent of the present invention includesligands attached to the colloidal particles in excess of and up to 200%of the C.E.C. of the colloid particles, resulting in greater efficacy ofthe antimicrobial agent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a scanning electron microscopy photograph of an untreatedHEPA filter.

FIG. 1B is a scanning electron microscopy photograph of a HEPA filtertreated with the antimicrobial agent of the present invention.

FIG. 2A is a scanning electron microscopy photograph of a filter treatedwith the antimicrobial agent of the present invention.

FIG. 2B is a scanning electron microscopy photograph of a filter treatedwith the antimicrobial agent of the present invention.

FIG. 3A is a photograph of a plate assay showing a comparison ofantimicrobial activity of the antimicrobial agents of the presentinvention.

FIG. 3B is a photograph of a plate assay showing a comparison ofantimicrobial activity of the antimicrobial agents of the presentinvention.

FIG. 4 is a plot of colony forming units versus untreated hectorite andhectorite treated with the antimicrobial agent of the present invention.

FIG. 5 is a plot of colony forming units versus untreated Laponite® andLaponite® treated with the antimicrobial agent of the present invention.

FIG. 6 is a plot of colony forming units versus HDTMA alone and HDTMAbound to Laponite® RD and Laponite® RDS.

FIG. 7 is a plot of colony forming units versus clay samples of HDTMAbound to Laponite® RD and HDTMA bound to BP with different HDTMAloadings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of controlling microbialgrowth on a material. The method includes applying to the material anantimicrobial agent containing colloid particles having one or moreligands having antimicrobial properties.

“Antimicrobial” describes the killing of, as well as the inhibition of,the growth of bacteria, yeast, fungi, algae, viruses, and mold.

Ligands having antimicrobial properties include compounds havingreactive inorganic cations, particularly those which have one or moreelectrons available for chemical reactions (i.e. transition metals) andcompounds containing organic cations known to have bactericidalactivity, for example, the antimicrobial effects of quaternary ammoniumcompounds, iodophor compounds, phenolics, alcohol, chlorine, peroxides,aldehydes and metals have been well documented. Disinfection,Sterilization and Preservation, 4th ed., Lea and Fabiger, Philadelphia(1991), which is hereby incorporated by reference. Ligands havingantimicrobial properties which are particularly desirable for use asligands in the present invention include quaternary ammonium compounds,transition metals, organo metallic compounds, perchlorates, chargedhalogen-containing compounds, charged organic peroxides, ionic polymers,ionic surfactants, and mixtures thereof. Especially desirable quaternaryammonium compounds include hexadecyltrimethyl ammonium bromide,trimethylphenyl ammonium chloride, and mixtures thereof. Especiallydesirable transition metals include copper, iron, manganese, zinc,silver, mercury, and mixtures thereof.

Any inorganic material exhibiting a combination of high surface area anda substantial ion exchange capacity, such as natural and synthetic clayminerals, are useful as colloid particles in the present invention.Preferred inorganic materials have surface areas ranging from 50-1000m²/gm, with surface areas of 500-800 m²/gm being especially desirable.Useful synthetic types of clay include a synthetic hectorite, which is alayered hydrous magnesium silicate, such as Laponite® (Southern ClayProducts, Gonzales, Tex.), a synthetic mica-montmorillonite, such asBarasym®, (Baroid Division, NL Industries, Houston, Tex.) and mixturesthereof. Useful natural types of clay include swelling clays such asaliettite, beidellite, nontronite, saponite, sauconite, stevensite,swinefordite, volkonskoite, yakhontovite, hectorite, montmorillonite(such as BP colloid), bentonite, and mixtures thereof. Other usefulmaterials (both synthetic and mineral) include, but are not limited to,zeolites, illite, chlorite, kaolinite, hydrotalcite, talc, halloysite,sepiolite, and palygorskite. Typically, the colloid particles of thepresent invention have a mean diameter of 1 nm to 1000 microns, withmean diameters of less than 2 microns being preferred.

In their unmodified state, clays have little deleterious effect onbacteria. Clay minerals typically have monovalent or divalent inorganiccations on the external and internal surfaces of the layer structurematerials. When these cations are exchanged with ligands havingantimicrobial properties, antimicrobial properties are imparted to theclay. The modified clays can be applied to substrates in the form of asurface coating or can be used as additives to the material to impartantimicrobial properties to the surface and the body of the material,respectively. Alternatively, the unmodified clay can be applied to asurface in the form of a surface coating, followed by contact with theligand having antimicrobial properties. The inorganic cations of theclay are then exchanged with the ligand having antimicrobial properties.Thus, antimicrobial properties are imparted to the surface.

Clays particularly useful as colloid particles in the present inventionare members of the smectite clay mineral group which are distinguishedby a large surface area (“S”), the ability to exchange cations,specified by the cation exchange capacity (“C.E.C.”), and by the abilityto swell in the presence of water and a variety of organic liquids,specified by the thickness of the clay layers as revealed by X-raydiffraction. Smectite clay minerals are layer structures which have anet negative charge as the result of substitutions of different cationswithin the individual mineral sheets. The high surface areas of thesematerials results from three factors: 1) the small particle size whichcreates a large external surface area, 2) the ability of the clay layersto expand by incorporating between adjacent layers water and variousorganic liquids which create a large internal surface area and 3) theplate-like morphology of the colloid particles. The negative charge onthe individual layers is balanced by cations, such as sodium, calcium,and magnesium, which are adsorbed onto both the external and internalsurfaces of the clay layers.

Examples of specific types of clays from the smectite mineral groupinclude: hectorite (“SHCa-1”, the Source Clay Minerals identificationcode) (provided by Source Clay Minerals Repository, University ofMissouri, Columbia, Mo.) with a C.E.C.=43.9 meq/100 gms and S=63.2m²/gm; Cheto montmorillonite (“SAz-1”) with a C.E.C.=120 meq/100 gms andS=97.4 m²/gm; Washington montmorillonite (“SWa-1”); Wyomingmontmorillonite (“SWy-2”) with a C.E.C=76.4 meq/100 gms, S=31.8 m²/gm;Laponite® RD with a C.E.C.=73 meq/100 gms and S=330 m²/gm; and Laponite®RDS with a C.E.C.=73 meq/100 gms and S=360 m²/gm.

To produce the antimicrobial agent of the present invention, the colloidparticles, either free or previously bound to a surface, are subjectedto ion exchange reactions whereby one or more ligands havingantimicrobial properties displace the normal endogenous inorganiccations or anions of the colloid particles. An important feature of thisinvention is that the modifying ligands are retained by the mineralsurfaces even after exhaustive washing. Thus, the efficacy of themodified colloid particles to act as antibacterial agents is not readilylost by leaching.

Specifically, the preparation of the antimicrobial agent is based on theprocess of ion exchange within the colloid particle. For example, clayshave exchangeable cations such as calcium, magnesium, potassium, sodium,and hydrogen on their internal and external surfaces. The cations on theclay mineral surfaces balance the net negative charge that occurs inclay minerals. Two adjacent negatively charged clay layers are heldtogether by the presence of the cations situated between the layers. Atypical clay particle can consist of from two to hundreds of suchlayers, all held together by the electrostatic bonds formed between thecations and the negatively charged surface of the clay layers. Thisbonding, although strong enough to keep the layers together, is muchweaker than the bonding between the atoms that form the layers. Thisweaker bonding between the layers plus the strong attraction of theinterlayer cations for water allows the entrance of water and othermolecules into the interlayer space. The endogenous inorganic interlayercations will be displaced by other inorganic or organic cationscontained in the liquid. Thus, if clay particles are suspended in aliquid dispersant containing cations, such as one or more ligands havingantimicrobial properties, there is an exchange of the endogenousinorganic interlayer cations of the clay for the cations in the liquiddispersant. Accordingly, these cations are referred to as exchangeablecations. It should also be noted that some colloid minerals have a netpositive charge and in such a case, the exchangeable ions would beanions.

In the case of organic cations, in accordance with the presentinvention, a quantity of antimicrobial ligand of up to 200% of theC.E.C. can be achieved for loading the colloid particles. Although notmeaning to be bound by theory, it is believed that this high loading isachieved due to the bonding of the one or more ligands havingantimicrobial properties to other ligands having antimicrobialproperties. More particularly, in the present invention, all surface andinterlayer cations are replaced by one or more ligands havingantimicrobial properties in an amount equivalent to 100% of the cationexchange capacity of the colloid particles. Further, other ligandshaving antimicrobial properties then bond to these ligands, such that aloading of an excess of and up to 200% of the cation exchange capacityof the colloid particles is achieved. The organic cation present inexcess of the C.E.C. is probably attached to the organo-clay byinteractions between the cation exchanged organic material and anorganic salt (U.S. Pat. No. 4,365,030 to Oswald, et al., which is herebyincorporated by reference).

To produce the antimicrobial agent, preferably, from 0.1 to 10 wt % ofcolloid particles, such as clay, is mixed with the liquid dispersant.The liquid dispersant contains sufficient ligand to satisfy fully orpartially the ion exchange capacity of the mineral colloid and to form asuspension containing the desired ligand having antimicrobialproperties. The liquid dispersant is typically water, but it can be anyliquid dispersant. The suspension is then thoroughly mixed and held forup to 24 hours at from 45° to 100° C. The suspension is thencentrifuged, decanted, and water washed three times, preferably withdistilled water. It is especially desirable to expose the colloidparticles to fresh solution three times to ensure maximum loading of theantimicrobial ligand. The colloid particles may be exposed to differenttypes of ligands in order to bind two or more different types of ligandsto the colloid particles. Preferably, a loading of up to 200% of thecation exchange capacity is achieved. For instance, if Wyomingmontmorillonite (“SWy-2”) is immersed in an aqueous solution ofhexadecyltrimethyl ammonium bromide (“HDTMA”), the organic cations ofthe HDTMA will exchange for the inorganic cations of the clay and theclay surface will become antimicrobial.

The antimicrobial agent can be applied to a material surface to impartantimicrobial properties to the surface. The antimicrobial agent can beapplied to the surface by any means, for example, by spraying,spreading, dipping, or brushing. As discussed above, the antimicrobialagent can be applied in a single step where the colloid particles havingone or more ligands with antimicrobial properties are applied to thesurface. Alternatively, a two step process can be used, where thecolloid particles are applied to the surface followed by contacting thecolloid particles with the one or more ligands having antimicrobialproperties. The surface can be any surface which it is desired to makeantimicrobial. Such surfaces include, but are not limited to, surfacesmade of cellulose, fiberglass, plastics, metals, glass, ceramic, wood,leather, cloth, and painted surfaces.

The thickness of the applied coating can be varied depending upon theneed. For example, when coating filters, ideally, a very thin coating ofthe antimicrobial agent should be applied. If the coating is too heavy,it is likely to block the filter pores and interfere with the filteringfunction. It is understood that one skilled in the art will be able toselect the appropriate thickness for their use.

In a preferred embodiment, the antimicrobial agent of the presentinvention is applied to a filter material to impart antimicrobialproperties to the filter. Coating the filter material with the modifiedantimicrobial clay can be achieved by various methods. Examples ofuseful methods of coating the filter material include 1) dipping thefilter material into an aqueous suspension of the modified clay, 2)spraying the filter material with a suspension of the modified clay, or3) by pre-adsorbing unmodified clay onto the filter material and thenperforming the cation exchange process by exposing the clay-treatedfilter material to an aqueous solution of the ligand havingantimicrobial properties. The time of exposure of the filter material tothe modified clay suspension can vary from a few seconds to hours, daysor longer depending on the application. This process may be repeated toapply more antimicrobial ligand to the surface.

Once coated onto the surface in question, the antimicrobial agent of thepresent invention does not readily leach out, eliminating the need forrepeated coatings. In addition, the ability of the antimicrobial agentto strongly bind to the coated surfaces indicates that no significantparticulate material is given off from such surfaces. Typicalapplications include applying the antimicrobial agent on air and waterfiltration devices, air ductwork, and fan housings to prevent microbialgrowth. Examples of other surfaces which can be coated with theantimicrobial agent of the present invention includes aquarium filtermaterial, automobile ventilation and air conditioner systems, bedsheets, blankets and bedspreads, buffer pads (abrasive and polishing),carpets and draperies, fiberfill for upholstery, sleeping bags, apparel,etc., where the fiber is cotton, natural down, nylon, polyester, rayonor wool, fiberglass ductboard, fire hose fabric, humidifier belts,mattress pads and ticking, underwear and outerwear, nonwoven disposablediapers, nonwoven polyester, outerwear apparel, disposable polyurethanefoam cushions, polyurethane foam for household, industrial andinstitutional sponges and mops, polyurethane foam for packaging andcushioning in contact applications, polyurethane foam used as a growthmedium for crops and plants, premoistened towelettes and tissue wipes,roofing materials—such as shingles, roofing granules, wood shakes, felt,stone and synthetic overcoats, sand bags, tents, tarpaulins, sails andropes, athletic and casual shoes, shoe insoles, shower curtains, socksto provide residual self-sanitizing activity against athlete's footfungus (i.e. Trichophyton mentagrophytes) on the sock, throw rugs,toweling made of 100 percent cotton, 100 percent polyester, and blendsof the two fibers, toilet tank and seat covers, umbrellas, upholsterymade of acetates, acrylics, cotton, fiberglass, nylon, polyester,polyethylene, polyolefins, polypropylene, rayon, spandex, vinyl andwool, vacuum cleaner bags and filters, vinyl paper or wallpaper,disposable wiping cloths that can be used for multiple purposes such asdusting or washing furniture, cars, walls, windows, floors, appliances,dishes, counter tops, etc., women's hosiery, and women's intimateapparel.

Alternatively, the antimicrobial agent can be mixed with a material toimpart antimicrobial properties to the material. For example, theantimicrobial agent can be incorporated into plastics to impartantimicrobial properties to the plastic The plastic can be used to makea wide variety of products including medical items (such as catheters,blood lines, implants, thermometers, bandages, surgical dressings,surgical apparel, respirators), food packaging, drug and cosmeticpackaging, eating utensils, shower curtains, bath mats and the like.Further, the antimicrobial agent may be added to grouts, cements, andconcretes to prevent unsightly mold or mildew from growing in or on thegrout, cement, and concrete, respectively. In addition, theantimicrobial agent is blended with other solid materials to producematerials such as sponges, toilet seats, rubber gloves, contact lenses,hearing aids, dusting powder, kitchen, bath, or laboratory shelf paper,carpet pads, pool covers, solar pool covers, cat litter, animal bedding,computer keyboard covers, computer keys, door knobs, tampons, sanitarynapkins, dental chairs, dryer sheets, mops, and dishcloths to impartantimicrobial properties to those materials.

Likewise, the antimicrobial agent is blended with liquids or gels as asuspension to impart antimicrobial properties to the liquid or gel. Forexample, the antimicrobial agent can be added to water for use as adisinfecting agent for cleaning walls, floors, counters, and tabletops.It can also be mixed into cosmetics and into paints. At higherconcentration levels, the antimicrobial agent can be mixed with adetergent and used as a surgical scrub. The antimicrobial agent can bemixed with paint or other coatings (such as polymers) and applied tosurfaces to prevent growth of microbials. In addition, the antimicrobialagent can be added to the water in cooling towers or can be included ina coating that is used to coat the surfaces in cooling towers to kill orinhibit the growth of bacteria.

In addition, the antimicrobial agent of the present invention can beapplied topically to both natural and synthetic fibers or can beincorporated directly into synthetic fibers during the manufacturingprocess. The fibers that can be used with the antimicrobial agent of thepresent invention include but are not limited to fibers made of wool,cotton, polyolefin, polyester, polyaramid, cellulose acetate, rayon,nylon, polystyrene, vinyls, acrylics, and polyurethanes.

The antimicrobial agent can be applied to the fiber or fabric by mixingit with a liquid such as water or other solvent or dispersant and thendipping, spraying or washing the fiber or fabric in the mixture. Asdiscussed above, alternatively, the fiber or fabric could first becontacted with the unmodified clay followed by contact with the ligandhaving antimicrobial properties. Suitable solvents that can be used ineither method to apply the antimicrobial agent include, but are notlimited to, aliphatic and aromatic solvents such as alcohols, benzene,toluene, xylene, and hexane. After applying the mixture, the fiber orfabric will be coated with the antimicrobial agent. Therefore, whenmicroorganisms come into contact with the fiber or fabric, theantimicrobial agent will kill or inhibit the growth of themicroorganism.

Examples of the type of fiber or fabric products contemplated include,but are not limited to, surgical gauze, padding on wound dressings,mattress covers, crib covers, bassinet covers, sailboat sails, tents,draw sheets, cubicle curtains, tooth brushes, hair brushes, fabric wallcovering, fabric base, fabric shower curtains, bath mats, athleticclothing such as underclothes, shirts, socks, shorts, pants, shoes andthe like, and hospital clothing such as examination robes, physicianscoats, and nurses uniforms.

The following examples are presented to further illustrate theinvention.

EXAMPLES

Materials

The naturally occurring clays were obtained from Dr. William D. Johns,Director, the Source Clay Minerals Repository, University of Missouri,Columbia Mo. 65201. These materials are described in “Data Handbook forClay Materials and other Non-metallic Minerals”, by H. van Olphen and J.J. Fripiat (Pergamon Press, New York, 1979). The synthetic clays(Laponite® RDS and Laponite® RD) and the natural BP were obtained fromSouthern Clay Products Inc., Gonzales Tex.

Example 1

Preparation of Antimicrobial Agent and Its Application to a Surface in aSingle Step

An antimicrobial HEPA filter/mineral colloid product can be achievedseveral ways. A preferred method is to perform a cation ion exchange ofa selected clay to produce a modified clay. For instance, 25 grams ofLaponite® RDS synthesized clay was added to a 600 ml bottle containing asolution of the desired ligand having antimicrobial properties. Thesolution concentration can vary from nearly saturated to very weak. Onecan adjust the amount of ligand so that there is just enough ligandpresent to do a complete exchange as determined by the cation exchangecapacity. To achieve maximum loading in excess of the C.E.C., a minimumof-three exposures to fresh solution is recommended. After an additionof antimicrobial solution, the suspension was thoroughly mixed andplaced in a warm (about 60° C.) oven overnight. This was followed bycentrifugation and decanting of the supernatant liquid. For maximumloading, this procedure was repeated two more times, each time beginningwith the addition of fresh antimicrobial solution. The final step wasdistilled water washing of the antimicrobial clay three times. Thesample of antimicrobial agent was then freeze dried and stored forsubsequent use. The antimicrobial agent was then added to water toprepare a 0.1 to 5% (wt/vol) suspension. The HEPA filter was placed intothe suspension and kept there for 30 minutes. After removing the coatedHEPA filter from the suspension it was rinsed rigorously and dried.

Example 2

Application of Antimicrobial Agent to a HEPA Filter in Two Steps

In the second method of preparation, untreated clay was first adsorbedto the HEPA filter and the cation exchange was then carried out. Asuspension of SWy-2 smectite clay was prepared. The maximum percent ofclay used to form a suspension was determined by the clay itself—in thiscase, no more than 4% wt/vol clay was used. If more were used, thesuspension would form a gel. Typically, from 0.1 to 1 wt % suspension isrecommended. The filter was dipped into the suspension for 30 minutes.The clay covered filter was then dipped into a cationic solution of from0.01 to 0.1 M of HDTMA to produce a filter coated with an antimicrobialagent.

Example 3

Deposition of Modified Clay Minerals on HEPA Filters

Experiments were designed to demonstrate that the modified clay materialcould be coated on the filter fibers so that any bacteria in physicalcontact with the filter would also contact one or more clay particles.

The antimicrobial colloid were prepared as follows. One sample wasprepared by adding 20 grams of Wyoming montmorillonite (“SWy-2”) to 100mls of 0.1M HDTMA aqueous solution. This suspension was placed into a58° C. oven overnight. The sample was then removed from the oven andseparated from the solution by centrifugation. Fresh aqueous solutioncontaining HDTMA was then added to the sample, and the mixture wasreturned to the oven, heated overnight, and separated by centrifugation.This procedure was repeated a third time. The sample was then separatedfrom the solution and washed with distilled water three times, returnedto the oven overnight, separated from wash water, frozen, and thenfreeze dried.

A second sample was prepared in the same manner with the exception ofusing 10 grams of the synthetic Laponite® RD clay and treating it with100 mls of a 0.1 M aqueous solution of CuCl₂.

Small pieces of high efficiency particulate arrest (“HEPA”) filtermaterial were placed in each of the suspensions for a period of 30minutes, after which the paper was removed. The suspensions were madefrom the HDTMA loaded clay and the Cu loaded clay, prepared as describedabove, by adding 2 grams of the antimicrobial agent to 200 ml ofdistilled water and stirring while the HEPA filter was in contact withthe suspension. Some filter paper pieces were dried directly and otherswere rinsed in distilled water before drying. The appearance anddistribution of the clay on the filter were determined by scanningelectron microscopy. Two morphologies were observed. In one, themontmorillonite clay occurred as small (micron sized) irregular tospherical particles, more or less uniformly distributed over the surfaceof the filter (shown in FIGS. 1A and 1B). FIG. 1A is the HEPA filterwith no treatment at a magnification of 3500 times. FIG. 1B is a HEPAfilter treated with 0.5% SWy-2/HDTMA at a magnification of 200 times.The second morphology (as shown in FIGS. 2A and 2B, which show HEPAfilters treated with 0.5% Laponite®/Cu at a magnification of 350 timesand 1000 times, respectively) showed thin sheets or films of claycoating the fibers and stretching between the fibers. This secondmorphology was most often observed for the clay types Laponite® RD andRDS and hectorite. The coverage of both samples appeared to be adequateso that a micron sized bacterium would physically contact one or moremodified clay particles. Further, there appeared to be no significantblockage of the pore system in the filter paper.

Calculation of the amount of clay actually deposited by this treatmenton the filter material indicated that enough clay was added to thefilter to provide a thickness of 1.3 microns, assuming uniform coverage.

Example 4

Antimicrobial Effects of Modified Clays when Mixed with a Material

The ability of various clays having ligands with antimicrobialproperties to prevent microbial growth was tested using an environmentalmicrobe source obtained from activated sewage sludge. The activatedsewage sludge was prepared as described in ASTM Method D5209-92.

The standard plate count assay described by the EPA MicrobiologicalMethods for Monitoring the Environment (EPA 600/8-78-017) was used todetermine the number of colony forming units (“cfu”) present in theactivated sludge. The antimicrobial effects of the various clays andmodified clays were assessed using the following modification of the EPAplating method. Clays and modified clays were added directly to themolten agar and mixed for 1 hour. This mixture was maintained in moltenform in a 48° C. water bath until use. One tenth milliliter (0.1 ml) ofmicrobial incubation suspension, prepared by diluting the activatedsewage sludge with medium to give 200-250 cfu, was added to the plateand 15 ml of the agar/test substance mixture pipeted onto the plate.This was mixed by swirling the plates. Triplicate plates for each samplewere prepared, incubated at 37° C. in a humidified atmosphere for twodays, and counted as in the EPA method. Two typical sets of plates areshown in FIGS. 3A and 3B. The plate assay results for antimicrobialactivity of copper-modified Laponite® RD (upper photograph) are comparedto HDTMA-modified Laponite® RD (lower photograph) in FIGS. 3A and 3B. Inboth cases, the tested concentration (% wt/vol) is given in the centerof the Figure for the respective plates of unmodified Laponite® RD (toprow of both photographs) and modified Laponite® RD (bottom row of bothphotographs). The concentration decreases from left to right in theFigures. The unmodified Laponite® RD had no effect on microbial colonycounts. A decreased number of microbial colonies are seen withincreasing concentrations of both copper- and HDTMA-modified Laponite®RD, and the HDTMA-modified Laponite® RD was more effective than thecopper-modified Laponite® RD. Inhibition of microbial growth is clearlydemonstrated by the reduction of the number of colonies on the plates.Control plates with no added microbes and with microbes but no additives(not shown) provide a negative control and a total count of the microbepopulation inoculated on the plates. This experiment provided anefficient testing of a wide variety of microbes at one time, and hasrelevance to the real world application for devices proposed forapplications for this technology. These experiments indicated that theefficacy of the modified clays depends upon the type of clay as well asthe modifying ligand.

The modified clays were prepared as follows. A series of natural andman-made clay minerals was modified by the exchange of cations withtransition metals and cationic organic antimicrobials. A summary of thetreated clays and the ligands bound to the clays surfaces is provided inTable I:

TABLE I Clay Metal Organics Hectorite Cu Mn Zn HDTMA Mont- Cu Fe Mn ZnHDTMA TMPA 4AP morillonite (SAz) Mont- Cu Fe Mn Zn HDTMA TMPA 4APmorillonite (SWy) Mont- Cu Fe Mn Zn HDTMA TMPA 4AP morillonite (SWa)Laponite ® Cu Fe Zn HDTMA RD where HDTMA is hexadecyltrimethyl ammoniumbromide TMPA is trimethylphenyl ammonium chloride 4AP is4-aminophenolhydrochloride

All of the clay minerals studied underwent exchange reactions wherebythe antimicrobial ligand shown in Table I displaced the normalendogenous cations and was retained by the mineral surfaces even afterexhaustive washing. Of the metals tested, copper-modified clays offeredthe greatest antimicrobial effect of all of the transition metalsstudied. The order of efficacy was Cu>Mn>Zn>Fe. The antimicrobialefficacy for copper-modified natural clays was in the orderhectorite>montmorillonite. Different varieties of the montmorilloniteclay exhibited different efficacy with the order being SAz>SWa>SWy. Atypical comparison of Cu-modified hectorite with untreated hectoriteclay is shown in FIG. 4.

Of the organic antimicrobials which were tested, HDTMA provided thegreatest antimicrobial activity of any antimicrobial modifier studied.The efficacy of HDTMA modified Laponite® RD was approximately 5 to 10times that of Cu modified Laponite® RD.

The synthetic clay, Laponite® RD, displayed similar or slightly higherefficacy when modified by either HDTMA or Cu when compared to themodified hectorite clay. Laponite® RD provided significant advantagesover the natural clay minerals with regard to its purity, consistency ofchemical composition, particle size, and ability to coat filter materialwith considerably less clumping than the natural clays. Theantimicrobial properties of modified Laponite® RD were greater than themost active modified natural clays, as shown in FIG. 5 (and compared toFIG. 4).

Example 5

Antimicrobial Potency of Ligand-Modified Laponites® Compared to PureAntimicrobial Ligand

The antimicrobial potency of HDTMA and HDTMA-modified Laponite® RD andLaponite® RDS was compared using the antimicrobial assay methodsdescribed in Example 4. HDTMA was tested over a concentration range of1.2×10⁻⁵ to 1.2×10⁻¹% by weight. Both HDTMA modified Laponite® RD andRDS were tested at 1.2×10⁻³ and 2.4×10⁻⁴ % HDTMA equivalents by weight.As seen in FIG. 6, both HDTMA Laponite® RD and HDTMA Laponite® RDS hadsimilar antimicrobial potency, which was indistinguishable from HDTMAalone. Thus, binding of HDTMA to the mineral colloid has no observabledetrimental effect on its antimicrobial potency.

Example 6

Antimicrobial Potency of Ligand-Modified Laponite® and BP with HDTMALoading

The effects of clay loading with an antimicrobial were determined underconditions which achieved varying amounts of antimicrobial on the clay.Both a natural clay, BP, a natural montmorillonite clay and a syntheticclay, Laponite® LRD, were studied. Both clays first were treated with anHDTMA concentration equivalent to the cation exchange capacity for theparticular clay. The treatment was repeated twice for a total of threetreatments. The treated clays received three warm water washings andwere freeze dried. The amounts of HDTMA associated with the clays aftereach of the treatments was estimated by a microwave ashing procedure.Samples were then tested for antimicrobial activity using a Pseudomonasaeruginosa assay in which the organism was spread on the surface of theplates at an inoculation density of 100 to 200 cfu per plate, andincubated overnight at 37° C.

The ashing results clearly show that a single treatment of Laponite® RDat a concentration equivalent to the C.E.C. results in an amount ofHDTMA bound which was essentially equivalent to the C.E.C. for the clay.Multiple treatments of the Laponite® RD clay with HDTMA resulted in thebinding of an amount of HDTMA that exceeds the CEC for that clay. In theclay treated two times, the loading of HDTMA was equal to 181% of theC.E.C. for Laponite® RD. When treated three times, the HDTMA loadingincreased to 200% of the C.E.C. The comparable values for the BP claywere 100% of the C.E.C. for the single treatment and 187% of the C.E.C.for the clay treated three times.

The increase in the amount of HDTMA associated with the clays correlateswith an enhanced antimicrobial effect for both the natural and syntheticclay. This is shown in FIG. 7. A single treatment of BP with HDTMA boundthereto (i.e. having ligand which fulfilled 100% of the CEC) resulted inno antimicrobial activity until the concentration of the treated clayexceeded 0.25% (w/v) of the medium. The BP treated three times withHDTMA (i.e. having ligand which fulfilled 187% of the CEC) hadantimicrobial activity beginning at 0.1%. Laponite® LRD treated threetimes with HDTMA (i.e. having ligand which fulfilled 200% of the CEC)had antimicrobial activity at all concentrations tested including0.025%. This clearly demonstrates the enhanced antimicrobial activitiesimparted to clays having ligand bound thereto, where the quantity ofligand attached to the clay is up to 200% of the CEC of the clay.

Example 7

Leachability of Antimicrobial Modifier from Filters

Pseudomonas aeruginosa (ATCC 27853) was obtained from the American TypeCulture Collection (Rockville, Md.). The organism was plated on NutrientBroth Agar (Difco Laboratories, Detroit, Mich.) at 10⁸ bacteria perplate, and incubated 24 hours at 37° C. to establish a confluent layerof Pseudomonas on the plate.

Laponite® RD modified with HDTMA was dip coated onto 1 cm diameter HEPAfilters from suspensions containing from 0.5% to 8.6% Laponite®RD/HDTMA. Filters were then washed exhaustively. Treated filters wereplaced on the layer of Pseudomonas aeruginosa and incubated overnight. Aclear zone surrounding the filter would indicate the migration of theantimicrobial from the filter.

No clear zone was detected for any of the four dip concentrations offilters studied. At the same time, there was no visible overgrowth ofthe filters by the bacteria. Similarly treated filters placed onnutrient broth agar inoculated simultaneously with 10⁸ bacteria perplate and similarly incubated revealed no zones of growth inhibition.Thus, HDTMA appeared to maintain its antimicrobial activity on thefilter without migrating from the filter.

Although the invention has been described in detail for the purpose ofillustration, it is understood that such detail is solely for thatpurpose, and variations can be made therein by those skilled in the artwithout departing from the spirit and scope of the invention which isdefined by the following claims.

What is claimed is:
 1. A method of controlling microbial growth on amaterial, said method comprising: applying to the material anantimicrobial agent comprising: colloid particles having an ion exchangecapacity and having attached a quantity of one or more ligands withantimicrobial properties, wherein the quantity of ligand attached to thecolloid particles is in excess of 100% and up to 200% of the ionexchange capacity of the colloid particles.
 2. A method-according toclaim 1, wherein the colloid particles are selected from the groupconsisting of natural clays, synthetic clays, zeolites, hydrotalcite,kaolinite, talc, halloysite, sepiolite, illite, chlorite, andpalygorskite.
 3. A method according to claim 2, wherein the colloidparticles are synthetic clay selected from the group consisting oflayered hydrous magnesium silicate, synthetic mica-montmorillonite, andmixtures thereof.
 4. A method according to claim 2, wherein the colloidparticles are natural clays selected from the group consisting ofhectorite, aliettite, beidellite, nontronite, saponite, sauconite,stevensite, swinefordite, volkonskoite, yakhontovite, montmorillonite,bentonite, and mixtures thereof.
 5. A method according to claim 1,wherein the ligand is selected from the group consisting of quaternaryammonium compounds, antimicrobial metals, organo metallic compounds,perchlorates, charged halogen-containing compounds, charged organicperoxides, ionic polymers, ionic surfactants, and mixtures thereof.
 6. Amethod according to claim 5, wherein the ligand is a quaternary ammoniumcompound selected from the group consisting of hexadecyltrimethylammonium bromide, trimethylphenyl ammonium chloride, and mixturesthereof.
 7. A method according to claim 6, wherein the one or moreligands comprise at least two ligands.
 8. A method according to claim 7,wherein the at least two ligands are different.
 9. A method according toclaim 5, wherein the antimicrobial metal is a transition metal selectedfrom the group consisting of copper, iron, manganese, zinc, silver,mercury, and mixtures thereof.
 10. A method according to claim 1,wherein the material is a surface to which the antimicrobial agent isapplied.
 11. A method according to claim 10, wherein the colloidparticles having one or more ligands having antimicrobial properties areapplied to the surface in a single step.
 12. A method according to claim10, wherein the surface is selected from the group consisting ofcellulose, fiber glass, plastics, metals, glass, wood, leather, ceramic,cloth, and painted surfaces.
 13. A method of claim 12, wherein thesurface is filter.
 14. A method according to claim 1, wherein thecolloid particles have a mean diameter of 1 nm to 1000 μm.
 15. A methodaccording to claim 14, wherein the colloid particles have a meandiameter of 1 nm to 2 μm.
 16. A method of controlling microbial growthin a material, said method comprising: mixing with the material colloidparticles having an ion exchange capacity and having attached one ormore ligands having antimicrobial properties, wherein the one or moreligands attached to the colloid particles is in a quantity in excess of100% and up to 200% of the ion exchange capacity of the colloidparticles.
 17. A method according to claim 16, wherein the colloidparticles are selected from the group consisting of natural clays,synthetic clays, zeolites, hydrotalcite, kaolinite, talc, halloysite,sepiolite, illite, chlorite, and palygorskite.
 18. A method according toclaim 17, wherein the colloid particles are synthetic clay selected fromthe group consisting of layered hydrous magnesium silicate, syntheticmica-montmorillonite, and mixtures thereof.
 19. A method according toclaim 17, wherein the colloid particles are natural clays selected fromthe group consisting of hectorite, aliettite, beidellite, nontronite,saponite, sauconite, stevensite, swinefordite, volkonskoite,yakhontovite, montmorillonite, bentonite, and mixtures thereof.
 20. Amethod according to claim 17, wherein the ligand is selected from thegroup consisting of quaternary ammonium compounds, organo metalliccompounds, ionic polymers, and ionic surfactants, and mixtures thereof.21. A method according to claim 20, wherein the ligand is a quaternaryammonium compound selected from the group consisting ofhexadecyltrimethyl ammonium bromide, trimethylphenyl ammonium chloride,and mixtures thereof.
 22. A method according to claim 21, wherein theone or more ligands comprise at least two ligands.
 23. A methodaccording to claim 22, wherein the at least two ligands are different.24. A method according to claim 21, wherein the antimicrobial agent isblended with other solid materials or with liquids as a suspension. 25.A method according to claim 16, wherein the colloid particles have amean diameter of 1 nm to 1000 μm.
 26. A method according to claim 25,wherein the colloid particles have a mean diameter of 1 nm to 2 μM. 27.An antimicrobial surface coated with colloid particles having an ionexchange capacity and having attached a quantity of one or more ligandshaving antimicrobial properties, wherein the quantity of ligand attachedto the colloid particles is in excess of 100% and up to 200% of the ionexchange capacity of the colloid particles.
 28. An antimicrobial surfaceaccording to claim 27, wherein the colloid particles are selected fromthe group consisting of natural clays, synthetic clays, zeolites,hydrotalcite, talc, halloysite, sepiolite, illite, chlorite, kaolinite,and palygorskite.
 29. An antimicrobial surface according to claim 27,wherein the colloid particles are synthetic clay selected from the groupconsisting of layered hydrous magnesium silicate, syntheticmica-montmorillonite, and mixtures thereof.
 30. An antimicrobial surfaceaccording to claim 28, wherein the colloid particles are natural claysselected from the group consisting of hectorite, montmorillonite,aliettite, beidellite, nontronite, saponite, sauconite, stevensite,swinefordite, volkonskoite, yakhontovite, and mixtures thereof.
 31. Anantimicrobial surface according to claim 28, wherein the ligand isselected from the group consisting of quaternary ammonium compounds,transition metals, organo metallic compounds, perchlorates, chargedhalogen-containing compounds, charged organic peroxides, ionic polymers,ionic surfactants, and mixtures thereof.
 32. An antimicrobial surfaceaccording to claim 28, wherein the ligand is a quaternary ammoniumcompound selected from the group consisting of hexadecyltrimethylammonium bromide, trimethylphenyl ammonium chloride, and mixturesthereof.
 33. An antimicrobial surface according to claim 32, wherein theone or more ligands comprise at least two ligands.
 34. An antimicrobialsurface according to claim 33, wherein the at least two ligands aredifferent.
 35. An antimicrobial surface according to claim 28, whereinthe ligand is a transition metal selected from the group consisting ofcopper, iron, manganese, zinc, silver, mercury, and mixtures thereof.36. An antimicrobial surface according to claim 27, wherein the colloidparticles have a mean diameter of 1 nm to 1000 μm.
 37. An antimicrobialsurface according to claim 36, wherein the colloid particles have a meandiameter of 1 nm to 2 μm.
 38. An antimicrobial surface according toclaim 28, wherein the surface is selected from the group consisting ofcellulose, fiber glass, plastics, metals, glass, wood, leather, ceramic,cloth, and painted surfaces.
 39. An antimicrobial surface according toclaim 38, wherein the surface is a filter.
 40. A material to whichantimicrobial properties have been imparted, wherein said materialcontains colloid particles having an ion exchange capacity and havingattached one or more ligands with antimicrobial properties, wherein theone or more ligands attached to the colloid particles is in a quantityin excess of 100% and up to 200% of the ion exchange capacity of thecolloid particles.
 41. A material according to claim 40, wherein thecolloid particles are selected from the group consisting of naturalclays, synthetic clays, zeolites, hydrotalcite, talc, halloysite,sepiolite, illite, chlorite, kaolinite, and palygorskite.
 42. A materialaccording to claim 41, wherein the synthetic clay is selected from thegroup consisting of layered hydrous magnesium silicate, syntheticmica-montmorillonite, and mixtures thereof.
 43. A material according toclaim 41, wherein the particles are natural clays selected from thegroup consisting of hectorite, aliettite, beidellite, nontronite,saponite, sauconite, stevensite, swinefordite, volkonskoite,yakhontovite, montmorillonite, and mixtures thereof.
 44. A materialaccording to claim 40, wherein the ligand is selected from the groupconsisting of quaternary ammonium compounds, organo metallic compounds,ionic polymers, ionic surfactants, and mixtures thereof.
 45. A materialaccording to claim 44, wherein the ligand is a quaternary ammoniumcompound selected from the group consisting of hexadecyltrimethylammonium bromide, trimethylphenyl ammonium chloride, and mixturesthereof.
 46. A material according to claim 45, wherein the one or moreligands comprise at least two ligands.
 47. A material according to claim46, wherein the at least two ligands are different.
 48. A materialaccording to claim 40, wherein the colloid particles have a meandiameter of 1 nm to 1000 μm.
 49. A material according to claim 48,wherein the colloid particles have a mean diameter of 1 nm to 2 μm. 50.An antimicrobial agent comprising: colloid particles having an ionexchange capacity and having attached one or more ligands havingantimicrobial properties, wherein the ligands attached to the colloidparticles is in a quantity in excess of 100% and up to 200% of the ionexchange capacity of the colloid particles.
 51. An antimicrobial agentaccording to claim 50, wherein the colloid particles are selected fromthe group consisting of natural clays, synthetic clays, zeolites,hydrotalcite, kaolinite, talc, halloysite, sepiolite, illite, chlorite,and palygorskite.
 52. An antimicrobial agent according to claim 51,wherein the colloid particles are synthetic clay selected from the groupconsisting of layered hydrous magnesium silicate, syntheticmica-montmorillonite, and mixtures thereof.
 53. An antimicrobial agentaccording to claim 51, wherein the colloid particles are natural claysselected from the group consisting of hectorite, aliettite, beidellite,nontronite, saponite, sauconite, stevensite, swinefordite, volkonskoite,yakhontovite, montmorillonite, bentoinite, and mixtures thereof.
 54. Anantimicrobial agent according to claim 50, wherein the ligand isselected from the group consisting of quaternary ammonium compounds,organo metallic compounds, ionic polymers, ionic surfactants, andmixtures thereof.
 55. An antimicrobial agent according to claim 54,wherein the ligand is a quaternary ammonium compound selected from thegroup consisting of hexadecyltrimethyl ammonium bromide, trimethylphenylammonium chloride, and mixtures thereof.
 56. The antimicrobial agentaccording to claim 55, wherein the one or more ligands comprise at leasttwo ligands.
 57. The antimicrobial agent according to claim 56, whereinthe at least two ligands are different.
 58. A complex comprising colloidparticles having an ion exchange capacity and having attached one ormore ligands, wherein the one or more ligands attached to the colloidparticles is in a quantity in excess of 100% and up to 200% of the ionexchange capacity of the colloid particles.
 59. A complex according toclaim 58, wherein the colloid particles are selected from the groupconsisting of natural clays, synthetic clays, zeolites, hydrotalcite,kaolinite, talc, halloysite, sepiolite, illite, chlorite, andpalygorskite.
 60. A complex according to claim 59, wherein the colloidparticles are synthetic clay selected from the group consisting oflayered hydrous magnesium silicate, synthetic mica-montmorillonite, andmixtures thereof.
 61. A complex according to claim 59, wherein thecolloid particles are natural clays selected from the group consistingof hectorite, aliettite, beidellite, nontronite, saponite, sauconite,stevensite, swinefordite, volkonskoite, yakhontovite, montmorillonite,bentonite, and mixtures thereof.
 62. A complex according to claim 59,wherein the ligand is selected from the group consisting of quaternaryammonium compounds, organo metallic compounds, ionic polymers, ionicsurfactants, and mixtures thereof.
 63. A complex according to claim 62,wherein the ligand is a quaternary ammonium compound selected from thegroup consisting of hexadecyltrimethyl ammonium bromide, trimethylphenylammonium chloride, and mixtures thereof.
 64. A complex according toclaim 63, wherein the one or more ligands comprise at least two ligands.65. A complex according to claim 64, wherein the at least two ligandsare different.
 66. A method of controlling microbial growth on a surfacecomprising: applying colloid particles having an ion exchange capacityto the surface in a first step and contacting the colloid particles withone or more ligands having antimicrobial properties in a second step,wherein the colloid particles are selected from the group consisting ofnatural clays, synthetic clays, zeolites, hydrotalcite, kaolinite, talc,halloysite, sepiolite, illite, chlorite, and palygorskite.
 67. A methodaccording to claim 66, wherein the colloid particles are synthetic clayselected from the group consisting of layered hydrous magnesiumsilicate, synthetic mica-montmorillonite, and mixtures thereof.
 68. Amethod according to claim 66, wherein the colloid particles are naturalclays selected from the group consisting of hectorite, aliettite,beidellite, nontronite, saponite, sauconite, stevensite, swinefordite,volkonskoite, yakhontovite, montmorillonite, bentonite, and mixturesthereof.
 69. A method according to claim 66, wherein the surface isselected from the group consisting of cellulose, fiberglass, plastics,metals, glass, wood, leather, ceramic, cloth, and painted surfaces. 70.A method according to claim 69, wherein the surface is a filter.
 71. Amethod according to claim 66, wherein the colloid particles have a meandiameter of 1 nm to 1000 μm.
 72. A method according to claim 71, whereinthe colloid particles have a mean diameter of 1 nm to 2 μm.
 73. A methodof controlling microbial growth on a surface comprising: applyingcolloid articles having an ion exchange capacity to the surface in afirst step and contacting the colloid particles with one or more ligandshaving antimicrobial properties in a second step, wherein the ligand isselected from the group consisting of quaternary ammonium compounds,antimicrobial metals, organo metallic compounds, perchlorates, chargedhalogen-containing compounds, charged organic peroxides, ionic polymers,ionic surfactants, and mixtures thereof.
 74. A method according to claim73, wherein the ligand is a quaternary ammonium compound selected fromthe group consisting of hexadecyltrimethyl ammonium bromide,trimethylphenyl ammonium chloride, and mixtures thereof.
 75. A methodaccording to claim 74, wherein the quantity of ligand attached to thecolloidal particles is in excess of 100% and up to 200% of the ionexchange capacity of the colloid particles.
 76. A method according toclaim 75, wherein the one or more ligands comprise at least two ligands.77. A method according to claim 76, wherein the at least two ligands aredifferent.
 78. A method according to claim 73, wherein the antimicrobialmetal is a transition metal selected from the group consisting ofcopper, iron, manganese, zinc, silver, mercury, and mixtures thereof.79. A method according to claim 73, wherein the surface is selected fromthe group consisting of cellulose, fiberglass, plastics, metals, glass,wood, leather, ceramic, cloth, and painted surfaces.
 80. A methodaccording to claim 76, wherein the surface is a filter.
 81. A methodaccording to claim 73, wherein the colloid particles have a meandiameter of 1 nm to 1000 μm.
 82. A method according to claim 81, whereinthe colloid particles have a mean diameter of 1 nm to 2 μm.